The object of the present invention is to provide a tread rubber composition having a base tread rubber combined with a system or package of performance-enhancing agents comprising silica, coupling agent, carbon black, and kaolin clay.
A wide variety of factors are taken into consideration in the art and science of formulating tire tread compositions. For example, the tires are formulated to achieve specific wet and dry handling characteristics, provide traction under snowy conditions, resist abrasion, and provide a quiet, comfortable ride while achieving suitable tire wear. Performance-enhancing agents are added to the base elastomer to help achieve the desired characteristics. Sometimes combinations of such agents can act synergistically and can function unexpectedly in collaboration.
It has been customary in the past to incorporate silica in tire tread compositions as a filler and also to enhance the performance characteristics of the tire, such as low rolling resistance, while improving adherence to wet and snow-covered ground, improving wear and aging properties while reducing noise.
While numerous patents relate to the state of the art with respect to the base polymer for tire treads, U.S. Pat. No. 5,227,425, to Rauline, relates more specifically to all-season, high-performance tires utilizing a specific type of silica to improve performance characteristics of the tires.
U.S. Pat. No. 4,522,970, to Scriver et al., is an example of a patent relating to sulfur cured, rubber tread compositions formulated to meet certain defined performance characteristics.
The present invention relates to a method of achieving unexpected stress/strain characteristics in tread compositions so as to reduce the low strain modulus of a tire tread without reducing the hardness or high strain modulus to the same degree. This contrasts with the customary relationship between these characteristics. More specifically, the compositions maintain wet and dry handling, abrasion resistance, and snow traction of a silica tread compound while improving ride comfort and impact damping.
The present invention is particularly suitable for tire treads intended for passenger cars, all-terrain vehicles, pick-up trucks, and motorcycles.
The above objects are met by the partial replacement of silica with a kaolin clay in conjunction with a silane coupling agent as a performance-enhancing system in an elastomeric tread composition.
In the method of the present invention low strain modulus is reduced without reducing the hardness or high strain modulus to the same degree in silica tread compounds by replacing from about 20 to about 40% of the total silica with an equal amount of kaolin clay to result in a performance-enhancing package of about 5 to 20 parts by weight of clay, about 20-50 parts by weight of a high structure, high surface area silica which preferably includes a silane coupling agent, and about 0-60 parts of highly structured, tread-grade carbon black, all per 100 parts of base elastomeric composition.